BMR Calculator

Basal Metabolic Rate — calories burned at rest

What Is BMR?

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain basic life functions — breathing, circulation, cell production, and body temperature regulation. It represents the minimum energy your body needs to survive if you spent the entire day in bed doing nothing.

For most people, BMR accounts for 60-75% of total daily calorie expenditure. This means the majority of the calories you burn each day are not from exercise, but from simply keeping your body alive. Understanding your BMR is the first step in calculating your total daily energy needs (TDEE).

BMR Formulas Compared

Our calculator offers three established formulas, each with its own strengths:

Mifflin-St Jeor (Recommended)

Developed in 1990, this is the most accurate formula for the general population according to the American Dietetic Association. It uses weight, height, age, and sex.

  • Men: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age) + 5
  • Women: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age) – 161

Harris-Benedict (Revised)

Originally from 1919 and revised in 1984, this formula is widely used in clinical settings. It tends to slightly overestimate BMR compared to Mifflin-St Jeor.

Katch-McArdle

This formula uses lean body mass instead of total weight, making it the most accurate option for individuals who know their body fat percentage. It is particularly useful for athletes or people with unusual body compositions.

Factors That Affect BMR

  • Muscle mass: More muscle = higher BMR. Each kg of muscle burns approximately 13 calories per day at rest, compared to 4.5 calories per kg of fat.
  • Age: BMR decreases by roughly 1-2% per decade after age 20, primarily due to loss of lean mass.
  • Sex: Men typically have higher BMR due to greater muscle mass and lower body fat percentage.
  • Genetics: Individual variation in BMR can be as much as 200-300 calories per day between people of similar size.
  • Hormones: Thyroid hormones play a major role. Conditions like hypothyroidism can significantly lower BMR.

From BMR to TDEE

Your BMR alone is not enough to plan your nutrition — you need to account for physical activity. Multiply your BMR by an activity factor (1.2 to 1.9) to get your TDEE. Use our TDEE Calculator for this step.

Next step: Use your BMR result in the TDEE Calculator to find your total daily calorie needs, then set targets with the Calorie Calculator.

Frequently Asked Questions

The Mifflin-St Jeor equation is considered the most accurate for the general population, as validated by the American Dietetic Association. If you know your body fat percentage, the Katch-McArdle formula may be more accurate, especially if you have above- or below-average muscle mass.
BMR is measured under strict conditions (12-hour fast, 8 hours of sleep, in a darkened room). RMR is less strict and typically 10-20% higher than BMR. Most calculators, including ours, technically estimate RMR but label it as BMR because the terms are commonly used interchangeably.
Yes, the most effective way is to increase your lean muscle mass through resistance training. Each additional kilogram of muscle raises your BMR by approximately 13 calories per day. While this may seem small, it accumulates over time and contributes to easier weight management.
BMR is primarily determined by body size (taller and heavier people have higher BMR), muscle mass, age, and sex. If your BMR seems unusually high or low, check your measurements and consider that individual genetic variation can cause differences of 200-300 calories.
Generally, no. Eating below your BMR for extended periods can cause metabolic adaptation, muscle loss, nutrient deficiencies, and hormonal disruption. Instead, create a moderate deficit of 300-500 calories below your TDEE (not your BMR). This allows for sustainable fat loss while preserving muscle.
BMR decreases approximately 1-2% per decade after age 20, primarily due to a reduction in lean muscle mass. A 50-year-old burns roughly 150-200 fewer calories at rest than a 20-year-old of the same size. Regular strength training can slow this decline significantly.